CD-ROM Appendix A, which is a part of the present disclosure, is a CD-ROM appendix consisting of twenty two (22) text files. CD-ROM Appendix A is a computer program listing appendix that includes a software program executable on a controller as described below. The total number of compact disks including duplicates is two. Appendix B, which is part of the present specification, contains a list of the files contained on the compact disk. The attached CD-ROM Appendix A is formatted for an IBM-PC operating a Windows operating system.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
These and other embodiments are further discussed below.
1. Field of the Invention
The present invention relates to an optical disk drive and, in particular, to an optical disk drive with a digital focus and tracking servo system.
2. Discussion of Related Art
The need for compact data storage is explosively increasing. The explosive increase in demand is fueled by the growth of multimedia systems utilizing text, video, and audio information. Furthermore, there is a large demand for highly portable, rugged, and robust systems for use as multimedia entertainment, storage systems for PDA""s, cell phones, electronic books, and other systems. One of the more promising technologies for rugged, removable, and portable data storage is WORM (write once read many) optical disk drives.
One of the important factors affecting design of an optical system (such as that utilized in a WORM drive) is the optical components utilized in the system and the control of actuators utilized to control the optical system on the disk. The optical system typically includes a laser or other optical source, focusing lenses, reflectors, optical detectors, and other components. Although a wide variety of systems have been used or proposed, typical previous systems have used optical components that were sufficiently large and/or massive that functions such as focus and/or tracking were performed by moving components of the optical system. For example, some systems move the objective lens (e.g. for focus) relative to the laser or other light source. It was generally believed that the relatively large size of the optical components was related to the spot size, which in turn was substantially dictated by designs in which the data layer of a disk was significantly spaced from the physical surface of the disk. A typical optical path, then, passed through a disk substrate, or some other portion of the disk, typically passing through a substantial distance of the disk thickness, such as about 0.6 mm or more, before reaching a data layer.
Regardless of the cause being provided for relative movement between optical components, such an approach, while perhaps useful for accommodating relatively large or massive components, presents certain disadvantages for more compact usage. These disadvantages include a requirement for large form factors, the cost associated with establishing and maintaining optical alignment between components which must be made moveable with respect to one another, and the power required to perform operations on more massive drive components. Such alignment often involves manual and/or individual alignment or adjustment procedures which can undesirably increase manufacturing or fabrication costs for a reader/writer, as well as contributing to costs of design, maintenance, repair, and the like.
Many early optical disks and other optical storage systems provided relatively large format read/write devices including, for example, devices for use in connection with 12 inch (or larger) diameter disks. As optical storage technologies have developed, however, there has been increasing attention toward providing feasible and practical systems which are of relatively smaller size. Generally, a practical read/write device must accommodate numerous items within its form factor, including the media, media cartridge (if any), media spin motor, power supply and/or conditioning, signal processing, focus, tracking or other servo electronics, and components associated or affecting the laser or light beam optics. Accordingly, in order to facilitate a relatively small form-factor, an optical head occupying small volume is desirable. In particular, it is desirable that the optical head have a small dimension in the direction perpendicular to the surface of the spinning media. Additionally, a smaller, more compact, optical head provides numerous specific problems for electronics designed to control the position and focus of the optical head.
Additionally, although larger home systems have little concern regarding power usage, portable personal systems should be low power devices. Therefore, it is also important to have a system that conserves power (e.g., by optically overfilling lenses) in both the optical system and the electronic controlling system.
Therefore, there is a need for an optical head and optical media drive system with a small form factor and, in addition, a servo system for controlling the optical head and optical drive system so that data can be reliably read from and written to the optical media.
In accordance with the present invention, a digital servo system for controlling the digital and tracking functions of an optical disk drive system is presented. The optical disk drive system includes a spin motor on which an optical media is positioned, an optical pick-up unit positioned relative to the optical media, an actuator arm that controls the position of the optical pick-up unit, and a control system for controlling the spin motor, the actuator arm, and the laser. The control system can include a read/write channel coupled to provide control signals to a servo system.
The optical media can be a relatively small-sized disk with readable data present on the surface of the disk. Furthermore, the optical disk may have a pre-mastered portion and a writeable portion. The pre-mastered portion is formed when the disk is manufactured and contains readable data such as, for example, audio, video, text or any other data that a content provider may wish to include on the disk. The writeable portion is left blank and can be written by the disk drive to contain user information (e.g., user notes, interactive status (for example in video games), or other information that the drive or user may write to the disk). Because there may be optical differences, for example in reflectivity, and in the data storage and addressing protocols between the pre-mastered portion of the disk and the writable portion of the disk, a control system according to the present invention may have different operating parameters in the different areas of the disk.
The optical pick-up unit can includes a light source, reflectors, lenses, and detectors for directing light onto the optical media. The detectors can include laser power feed-back detectors as well as data detectors for reading data from the optical media. The optical pick-up unit can be mechanically mounted on the actuator arm. The actuator arm includes a tracking actuator for controlling lateral movement across the optical media and a focus actuator for controlling the position of the optical pick-up unit above the optical medium. The tracking and focus actuators of the optical pick-up unit are controlled by the controller.
The servo system includes various servo loops for controlling the operation of aspects of the optical disk drive, for example the spin motor, the optical pick-up unit, and the controller. The servo loops, for example, can include combinations of a tracking servo loop and a focus servo loop.
A method of controlling the position of an optical pick-up unit according to the present invention can include calculating an error signal from digitized signals received from detectors in an optical pick-up unit mounted on an actuator arm; adding an offset value to the error signal to form a biased error signal; digitally amplifying the biased error signal to form an amplified signal; digitally filtering a pre-filtered signal related to the amplified signal to form a filtered signal; and driving the actuator arm in response to a digital control signal related to the filtered signal to control the position of the optical pick-up unit.
The error signal can be a tracking error signal or a focus error signal. If the error signal is a tracking error signal, then the control signal is utilized to control the tracking position (i.e., the position in a plane parallel with the surface of an optical media) of the optical pick-up unit. If the error signal is a focus error signal, then the control signal is utilized to control the focus position (i.e., the height above the optical media) of the optical pick-up unit.
In some embodiments, the digital filtering can include a low frequency integrator. In some embodiments, the digital filtering can include a phase lead filter. In some embodiments, the digital filtering can include a notch filter. Further, in some embodiments a sample integrity test filter can be included. Further, the digital servo system can include loop gain amplification. Further, an inverse non-linearity function can also be included. In a focus servo system, a correction for TES to FES cross-coupling can also be included by subtracting a fraction of the tracking error signal (TES) to the focus error signal (FES).
A servo system according to the present invention can also process signals received from detectors in the optical pick-up unit by, for example, converting optical signals received from the optical pick-up unit into voltage signals; providing an analog amplification and a bias offset to the voltage signals; digitizing the amplified voltage signals; and decimation filtering the digitized voltage signals to form the digitized signals.
A servo system according to the present invention, then, can include detectors positioned in an optical pick-up unit, an analog processor coupled to receive signals from the detectors and produce digitized signals, and a digital processor receiving the digitized signals and producing a control signal for controlling the position of the optical pick-up unit. In some embodiments, the detector includes optical detector elements. The digital processor, which can include digital signal processors and microprocessors executing an algorithm that calculates an error signal from the digitized signals, adds offsets and amplifies the error signals, filters the error signals, and calculates the control signal. In some embodiments, the error signal is a focus error signal. In some embodiments the error signal is a tracking error signal.
In some embodiments, each of the detectors can include a center element and two outside elements. A focus error signal, for example, can be obtained from the difference of the sum of signals from the two outside elements and the signal from the center element. A tracking error signal can be obtained from differences in the signals between the two outside elements.
These and other embodiments of the invention are further described below with respect to the following figures.